Manchester United manager Sir Alex Ferguson has upped the stakes ahead of Sunday's derby, claiming three points against Manchester City would be one of his side's greatest victories.

Ferguson was openly critical of his defence after United's 4-3 win over Reading at the weekend, and with the likes of Carlos Tevez, Sergio Aguero and Mario Balotelli heading City's attack, the Scot has urged his side to learn from their mistakes.

Victory at Etihad Stadium would see United move six points clear at the top of the Premier League, and Ferguson sees the game as a key fixture in the season.

"If we win [on Sunday] it will be one of our best ever results," Ferguson told MUTV. "They are a really good, powerful team with massive players. It won't be easy and if we defend like we did at Reading we'll be in trouble.

"The important thing for us is to take lessons from the mistakes we're making and do something about it. We need to find a solution."

Ferguson, who has suggested that both Nemanja Vidic and Tom Cleverley are unlikely to feature this weekend, refused to admit that the Premier League title race was once again a straight shootout between the two Manchester rivals.

"At this time in the season you can't really say it's a two-horse race," Ferguson said. "If you think back we were 12 points behind Chelsea at one point and when Arsenal beat us in the league in 1998 we were 11 points clear."